Page - 149 - in Book of Full Papers - Symposium Hydro Engineering

The service spillway discharge would be 8,382 m3/s (296,000 ft3/s) with Lake Oroville at Elevation 279.5 m (917 ft) and all gates fully open [2]. 2.3. EMERGENCY SPILLWAY The emergency spillway is also located on the right abutment, to the right of the service spillway. The emergency spillway consists of two sections: a 284-m (930-ft) long, concrete, gravity, ogee weir on the left side, and a 244-m (800-ft) long broad-crested, concrete weir on the right side. The crests of both sections are at Elevation 274.6 m (901 ft), which is 0.3 m (1 ft) above the maximum normal operating reservoir level, Elevation 274.3 m (900 ft). The maximum height of the emergency spillway crest structure is about 15.2 m (50 ft) in the ogee weir (left) section. Water flowing over the emergency spillway crest structure would then pass over natural terrain down to the Feather River. The emergency spillway discharge would be 9,910 m3/s (350,000 ft3/s) with the reservoir at 279.5 m Elevation (917), which corresponds to a depth of flow over the crest weirs of about 4.88 m (16 ft) [2]. 2.4. SPILLWAY OPERATION HISTORY The service spillway gates are operated to control reservoir levels in accordance with the operation plan for the facility. The gates were first operated in 1969, within a year after the project was completed, with a maximum service spillway discharge of almost 2,320 m/s2 (82,000 ft3/s) in that year. Service spillway operations vary from year to year, depending primarily on snowpack in the Feather River Basin. The operating record includes extended periods of time when spillway gate operation was not required, e.g. 1975 through 1979, 1987 through 1992, and 2007 through 2010. Of the 48 years from 1969 through 2016, there were 23 years when the service spillway did not operate, 11 years during which discharges exceeded 1,420 m3/s (50,000 ft3/s), and three years during which discharges exceeded 2,830 m3/s (100,000 ft3/s). The record service spillway discharge was 5,530 m3/s (160,000 ft3/s), in 1997. From 1998 through 2016, spillway discharges exceeded 312 m3/s (11,000 ft3/s) in only three years: about 1,700 m3/s (60,000 ft3/s) in 2005, 2,100 m3/s (74,000 ft3/s) in 2006, and 878 m3/sec (31,000 ft3/s) in 2011. The emergency spillway was activated for the first time in the project’s history during the February 2017 flood event and spillway incident. 149